Qualitative representation of the field distribution at the Lyot plane for a VC of charge l_p = 2 (left) and l_p = 4 (right), as a function of the (n,m) integer pair of the input Zernike polynomial Z_j. In the column m = 0, only one term defines the field distribution and is depicted in green. For all the other cases, two terms contribute to the electric field, represented in cyan and pink. In the case in which both terms are superimposed either outside or inside the pupil, these colors are mixed into a purple hue (see, for instance, the coma for the charge l_p = 2 vortex, or the tip-tilt for the charge l_p = 4 vortex).